The present invention relates to a seal device for a Lysholm compressor to be used for sealing a rotor shaft of the compressor.
FIGS. 1 and 2 schematically illustrate a Lysholm compressor 23 which comprises a male rotor 1 with helical crests 1a on its periphery and a female rotor 2 with helical valleys 2a on its periphery for meshing with the crests 1a of the rotor 1. The rotors 1 and 2 mesh with each other and are rotatably accommodated in a casing 3. The rotors 1 and 2 are rotated in directions of arrows r and r', respectively, in FIG. 1 to suck the air 4 from an axial end of the compressor. The air 4 is then compressed between the rotors 1 and 2 and is discharged from the other axial end of the compressor in a direction perpendicular to the axis. As shown in FIG. 2, the rotors 1 and 2 are supported at their respective shafts 5, 6 and 7, 8 protruding from opposite axial ends of the rotors 1 and 2, by the casing 3 through bearings 9, 10 and 11, 12, respectively.
An input shaft 13 is arranged in the casing 3 on a side opposite to the air suction side, i.e. at the left in FIG. 2, and a pulley 14 for the compressor is arranged on an outer end of the input shaft 13.
The input shaft 13 is rotatably supported at its outer end on the pulley 14 by a bearing 15 and at its inner end in the casing 3 by a bearing 16.
Interposed between the inner end of the input shaft 13 and the shafts 5 and 7 is a speed increasing device 17 which comprises a speed increasing gear 18 fixed to the inner end of the input shaft 13, a speed increasing pinion 19 fixed to the shaft 7 of the rotor 2 and meshing with the gear 18, a female-rotor timing gear 21 fixed to a boss 20 of the pinion 19 and a male-rotor timing gear 22 fixed to the shaft 5 of the rotor 1 and meshing with the gear 21,
Lubricant is filled in the speed increasing device 17 and in a space at the right in FIG. 2 surrounding the shafts 6 and 8. In order to prevent leakage of the lubricant toward the rotors 1 and 2, seal devices 24 are provided respectively between the rotor 1 and the bearings 9 and 10 of the shafts 5 and 6 and between the rotor 2 and the bearings 11 and 12 of the shafts 7 and 8.
As shown in FIG. 3, which is an enlarged cross-sectional view, the seal device 24 comprises a seal ring 25 and a maintaining ring 26 arranged peripherally of the shaft 5, 6, 7 or 8. The seal ring 25 is non-rotatably supported in the casing 3 and the maintaining ring 26 is rotatably supported on the shaft 5, 6, 7 or 8. The seal ring 25 is pressed against the maintaining ring 26 by a spring 27 to attain complete sealing at contact surface between the rings 25 and 26, thereby preventing oil leakage.
The seal ring 25 is made of sintered carbon. The pressing surface of the seal ring 25 is polished to have fine surface roughness of less than about 0.8.mu. and is pressed against the maintaining ring 26 which is made of metal and which is polished to similar degree of surface roughness, thereby assuring full sealing between the rings 25 and 26. Here, the surface roughness is based on the height profile irregularities at ten points, R.sub.z, (see ISO 468-1982), .mu. representing a micron.
The pulley 14 shown in FIG. 2 is coupled to an output shaft of an engine via a belt 28 so as to transmit rotation of the output shaft of the engine to the input shaft 13.
As shown in FIG. 4, the belt 28 is connected on a crank pulley 29 fixed to the output shaft of the engine, and tension is applied to the belt 28 by a tensioner 30. Rotation of the output shaft of the engine is transmitted to the pulley 14 as well as further pulleys 31 and 32 provided for other auxiliaries or accessories.
When the seal ring 25 in FIG. 3 is kept to have smooth surface with surface roughness of less than about 0.8.mu., an oil film 33 is formed as shown in FIG. 5 between the non-rotating seal ring 25 and the rotating maintaining ring 26. This oil film 33 provides a minute gap L of about 5.mu. between the surfaces of the rings 25 and 26, thereby excluding oil leakage.
As already explained in connection with FIG. 4, the crank pulley 29 is rotated by the output shaft of the engine. The rotating speed of the engine will suddenly change. When the rotating speed of the maintaining ring 26 is suddenly increased via the belt 28, input shaft 13 and speed increasing device 17 in FIG. 2, high shearing force is suddenly applied on the finely polished or mirror-finished surface of the seal ring 25 by the oil film 33 shown in FIG. 5. Then, pores 34 present within the carbon seal ring 25 may cause cracking and cracks may be propagated.
As a result, a swelling known as blister 35 may occur on the surface of the seal ring 25 as shown in FIG. 6.
When the blister 35 is formed on the surface of the seal ring 25, the ring 25 is pressed by bounce of the oil film 33 in a direction away from the maintaining ring 26 as shown by an arrow P in FIG. 7. As a result, distance L' between the surfaces of the rings 25 and 26 is widened such that the distance L from the top of the blister 35 to the surface of the maintaining ring 26 is about 5.mu.. This will lead to oil leakage and deterioration of seal effect.
It is therefore an object of the present invention to provide a seal device for a Lysholm compressor which prevents the occurrence of blister to enhance seal effect.